Page:Quarterly Journal of the Geological Society of London, vol. 25.djvu/115

 The brown beds at the top of the escarpment are so irregular in their appearance that it is difficult to continue the section ; probably there are from 20 to 30 feet more of similar beds at the top of the plateau. The lowest bed (No. 1) appears to be that regarded as forming the top of the chalk by Dr. Figari Bey.

One of the most marked horizons in the whole section is what may be called the big-Nummulite bed, which contains the large species of Nummulites, examples of which may be found up to 2-1/4 inches in diameter. It lies about 80 feet below the junction of the white and brown beds, a position corresponding to the lower part of bed No. 4 in the above section.

Along the lateral valleys the gypsum-marls (No. 9) have been subjected to considerable atmospheric degradation, and large pieces of celestine are common in the talus formed by the waste of the hill. They are partially rolled, of a dull bluish-grey colour, and compact, forming either long prismatic forms, from the combination OP. oo Poo, or similar combinations tapering to one end, having formed part of a spheroidal aggregate of crystals, terminating externally by the planes of the diagonal prism oo P. On examining the cliff-section these spheroids or nodules are found in place in the sandy limestones and marls, together with fibrous gypsum. They show a roughly stellar aggregate of crystals, with a dull earthy centre, the largest examples being about 4 inches in diameter.

The following (p. 42) is a measured section of the principal celestine-bearing beds where they are well-developed ; it is taken in a gulley behind the main escarpment. In addition to these there is another bed with nodules of celestine, a few feet below bed No. 10.

About 30 feet below the junction of the white and brown Nummulitic beds there is a very singular development of celestine crystals in the hollows of a white fossiliferous limestone. They are mostly long prisms of the open form OP. Poo, often of considerable size (up to 4 or 5 inches in length), and almost always very rough and decomposed about the ends in the plane of the prismatic faces oo P. Besides the simple crystals, macled groups of two, arranged similarly to the diagonal cuneiform twins of Staurolite, and similar combinations of three or more crystals of greater complexity are found, although not quite so abundantly as the former. In either case, however, the surfaces of the crystals generally seem to be incrusted with fragments of shells, Bryozoa, and small Nummulites, as though they had formed points of adhesion for these organisms. But that this is not the case, is proved on closer inspection, as the shells often pass right through the crystal; and on subjecting some of the more perfect specimens to cleavage, transparent plates were obtained with Nummulites enclosed. It is evident, therefore, that the fossils must have been entangled in the crystals at the time of their formation, and that their subsequent exposure is due to the action of solvents, which have removed the sulphate of strontia, leaving the carbonate of lime, forming the shells and Nummulites, untouched. The hollows in which the crystals are found are generally empty, owing to the original contents having been partly removed by the action of the atmosphere ;